Say I have 2 creatures enchanted with Lure or 2 Taunting Elves attacking: Does my opponent get to choose which of their creatures blocks each one or do I? What if one of those attacking creatures also has flying but the other does not? If one of my opponent's creatures can block multiple creatures, must they block both?
Answers to your questions, as covered by this rule:
Nothing in the Lure ability says that you get to choose. The defender has to follow the maximum number of requirements without disobeying any restrictions.
One of the restrictions on the defenders, barring any additional abilities, is that they may only block one creature. Therefore, the defender must block one of your attackers and may choose which one to block, as that fulfills the maximum number of requirements without disobeying the restriction of only being able to block one creature.
Obviously, if a defender is unable to block creatures with flying (that is a restriction) that defender must block the one it is able to block.
If a creature is able to block multiple creatures it must meet the maximum number of requirements that could be obeyed, therefore it must block both creatures if able. (Unless that blocker is something like an Anurid Swarmsnapper… as rule 509.1c states, the defender is not required to pay a cost to increase the number of requirements obeyed.)